Hydraulic actuators are generally known. A typical hydraulic actuator includes a motor that drives a hydraulic pump to move fluid from a reservoir to a hydraulic cylinder for actuating a rod of the actuator. When the motor is driven in a first rotational direction, the hydraulic fluid moved by the hydraulic pump extends the rod. When the motor is driven in a second rotational direction, opposite to the first rotational direction, the hydraulic fluid moved by the hydraulic pump retracts the rod.
Depending on the configuration, the hydraulic cylinder may retract the rod to raise a load or extend the rod to lower the load. For example, the hydraulic cylinder may be disposed on a portion of a lawn mower and extend to lower a mower deck in a gull-wing motion. Due to the substantial weight of the load in such devices, as the load is lowered, the load tends to force the hydraulic cylinder to move faster than the hydraulic pump can provide flow to the hydraulic cylinder.
The lack of sufficient flow from the hydraulic pump may reduce pressure in a fluid flow path connected to a front side of the cylinder causing a corresponding poppet of a fluidly connected check valve to close against a seat of the check valve. Soon after the poppet closes the pump may re-pressurize the fluid causing the poppet to re-open to again lower the fluid pressure, which causes the poppet to re-close until the pump can re-pressurize the fluid. The repeated opening and closing of the poppet causes the hydraulic cylinder to become unstable and bounce or “chatter” as the load is lowered.